Sara De Brouwer

Ghent University, Gand, Flemish, Belgium

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Publications (14)125.81 Total impact

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    ABSTRACT: Activating ALK mutations are present in almost 10% of primary neuroblastomas and mark patients for treatment with small molecule ALK inhibitors in clinical trials. However, recent studies have shown that multiple mechanisms drive resistance to these molecular therapies. We anticipated that detailed mapping of the oncogenic ALK driven signaling in neuroblastoma can aid to identify potential fragile nodes as additional targets for combination therapies. To achieve this goal, transcriptome profiling was performed in neuroblastoma cell lines with ALKF1174L or ALKR1275Q hotspot mutations, ALKamp or ALKwt following pharmacological inhibition of ALK using four different compounds. Next, we performed cross-species genomic analyses to identify commonly transcriptionally perturbed genes in MYCN/ALKF1174L double transgenic versus MYCN transgenic mouse tumors as compared to the mutant ALK-driven transcriptome in human neuroblastomas. A 77-gene ALK signature was established and successfully validated in primary neuroblastoma samples, in a neuroblastoma cell line with ALKF1174L and ALKR1275Q regulable overexpression constructs and in other ALKomas. In addition to the previously established PI3K/AKT/mTOR, MAPK/ERK and MYC/MYCN signaling branches, we identified that mutant ALK drives a strong upregulation of MAPK negative feedback regulators and upregulates RET and RET-driven sympathetic neuronal markers of the cholinergic lineage. We provide important novel insights into the transcriptional consequences and the complexity of mutant ALK signaling in this aggressive pediatric tumor. The negative feedback loop of MAPK pathway inhibitors may impact on novel ALK inhibition therapies while mutant ALK induced RET signaling can offer novel opportunities for testing ALK-RET oriented molecular combination therapies. Copyright © 2015, American Association for Cancer Research.
    Full-text · Article · Mar 2015 · Clinical Cancer Research
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    ABSTRACT: Restoration of the antitumor activity of p53 could offer a promising approach for the treatment of neuroblastoma. MicroRNAs (miRNAs) are important mediators of p53 activity, but their role in the p53 response has not yet been comprehensively addressed in neuroblastoma. Therefore, we set out to characterize alterations in miRNA expression that are induced by p53 activation in neuroblastoma cells. Genome-wide miRNA expression analysis showed that miR-34a-5p, miR-182-5p, miR-203a, miR-222-3p, and miR-432-5p are upregulated following nutlin-3 treatment in a p53 dependent manner. The function of miR-182-5p, miR-203a, miR-222-3p, and miR-432-5p was analyzed by ectopic overexpression of miRNA mimics. We observed that these p53-regulated miRNAs inhibit the proliferation of neuroblastoma cells to varying degrees, with the most profound growth inhibition recorded for miR-182-5p. Overexpression of miR-182-5p promoted apoptosis in some neuroblastoma cell lines and induced neuronal differentiation of NGP cells. Using Chromatin Immunoprecipitation-qPCR (ChIP-qPCR), we did not observe direct binding of p53 to MIR182, MIR203, MIR222, and MIR432 in neuroblastoma cells. Taken together, our findings yield new insights in the network of p53-regulated miRNAs in neuroblastoma.
    Full-text · Article · Mar 2015 · Scientific Reports
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    ABSTRACT: Restoration of the antitumor activity of p53 could offer a promising approach for the treatment of neuroblastoma. MicroRNAs (miRNAs) are important mediators of p53 activity, but their role in the p53 response has not yet been comprehensively addressed in neuroblastoma. Therefore, we set out to characterize alterations in miRNA expression that are induced by p53 activation in neuroblastoma cells. Genome-wide miRNA expression analysis showed that miR-34a-5p, miR-182-5p, miR-203a, miR-222-3p, and miR-432-5p are upregulated following nutlin-3 treatment in a p53 dependent manner. The function of miR-182-5p, miR-203a, miR-222-3p, and miR-432-5p was analyzed by ectopic overexpression of miRNA mimics. We observed that these p53-regulated miRNAs inhibit the proliferation of neuroblastoma cells to varying degrees, with the most profound growth inhibition recorded for miR-182-5p. Overexpression of miR-182-5p promoted apoptosis in some neuroblastoma cell lines and induced neuronal differentiation of NGP cells. Using Chromatin Immunoprecipitation-qPCR (ChIP-qPCR), we did not observe direct binding of p53 to MIR182, MIR203, MIR222, and MIR432 in neuroblastoma cells. Taken together, our findings yield new insights in the network of p53-regulated miRNAs in neuroblastoma. U nder normal physiological conditions, MDM2 inhibits p53 by binding to its transcriptional activation domain 1 and by promoting its degradation via an E3-ubiquitin ligase activity 2 maintaining low steady-state levels of p53 expression. In response to various intrinsic or extrinsic stress signals, p53 is relieved from MDM2 inhibition leading to activation of the p53-controlled program of cell cycle arrest, cellular senescence or apoptosis. The p53 transcription factor controls a transcriptional network of p53-responsive genes and non-coding RNAs that collectively drive a given cellular response 1,3. New insights into the mechanisms by which p53 regulates cellular growth/apoptosis/senescence can be gained by identifying up or downregulated microRNAs (miRNAs) upon p53 activation. MiRNAs are small non-coding RNAs of 18–23 nucleotides in length that regulate gene expression at the post-transcriptional level mainly by binding in a sequence specific manner to the 39-untranslated regions (39UTRs) of messenger RNAs (mRNAs) and negatively regulating their expression 2,4. MiRNAs have been shown to be an integral component of the p53 pathway regulating multiple p53-controlled biological processes 5. Altered expression of tumor suppressive or oncogenic miRNAs can disrupt the p53-miRNA axis enhancing tumor growth or decreasing tumor proliferation. Although several miRNAs such as the miR-34 family 6 , miR-145 7 , miR-107 8 , miR-192, and miR-215 9 have been shown to be essential components of the p53 tumor suppressor network, the spectrum of p53 regulated miRNAs in neuroblastoma remains to be established in detail. Neuroblastoma is the most common extra-cranial solid childhood cancer. Although less than 2% of neuro-blastoma tumors diagnosed harbor a TP53 (p53) mutation, p53 fails to act as an effective tumor suppressor 10. In consideration of the fact that the paradigm of cancer treatment shifts from broadly acting genotoxic agents to biologically targeted therapies, the prospect of targeting MDM2 to reactivate p53 holds promise for the molecular therapy of neuroblastoma. A small molecule antagonist of MDM2, nutlin-3, can restore p53 function by selectively disrupting the interaction between MDM2 and p53. Consequently p53 accumulates and induces the expression of its target genes. We have previously shown that nutlin-3 has profound effects on neuroblastoma cells and xenografts leading to premature senescence, apoptosis, and neuronal differentiation 2,11. In this study we performed a global megaplex profiling of 750 miRNAs in neuroblastoma cells after p53 activation and subsequently identified differentially expressed miRNAs. A neuroblastoma cell line lentivirally transduced with a short hairpin RNA against human p53 or murine p53 (negative control) was used to identify OPEN
    Full-text · Article · Mar 2015 · Scientific Reports
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    ABSTRACT: Two surveys of over 1,700 publications whose authors use quantitative real-time PCR (qPCR) reveal a lack of transparent and comprehensive reporting of essential technical information. Reporting standards are significantly improved in publications that cite the Minimum Information for Publication of Quantitative Real-Time PCR Experiments (MIQE) guidelines, although such publications are still vastly outnumbered by those that do not.
    Full-text · Article · Nov 2013 · Nature Methods
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    ABSTRACT: Two surveys of over 1,700 publications whose authors use quantitative real-time PCR (qPCR) reveal a lack of transparent and comprehensive reporting of essential technical information. Reporting standards are significantly improved in publications that cite the Minimum Information for Publication of Quantitative Real-Time PCR Experiments (MIQE) guidelines, although such publications are still vastly outnumbered by those that do not.
    Full-text · Article · Nov 2013 · Nature Methods
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    ABSTRACT: Measuring messenger RNA (mRNA) levels using the reverse transcription quantitative polymerase chain reaction (RT-qPCR) is common practice in many laboratories. A specific set of mRNAs as internal control reference genes is considered as the preferred strategy to normalize RT-qPCR data. Proper selection of reference genes is a critical issue, especially in cancer cells that are subjected to different in vitro manipulations. These manipulations may result in dramatic alterations in gene expression levels, even of assumed reference genes. In this study, we evaluated the expression levels of 11 commonly used reference genes as internal controls for normalization of 19 experiments that include neuroblastoma, T-ALL, melanoma, breast cancer, non small cell lung cancer (NSCL), acute myeloid leukemia (AML), prostate cancer, colorectal cancer, and cervical cancer cell lines subjected to various perturbations. The geNorm algorithm in the software package qbase+ was used to rank the candidate reference genes according to their expression stability. We observed that the stability of most of the candidate reference genes varies greatly in perturbation experiments. Expressed Alu repeats show relatively stable expression regardless of experimental condition. These Alu repeats are ranked among the best reference assays in all perturbation experiments and display acceptable average expression stability values (M<0.5). We propose the use of Alu repeats as a reference assay when performing cancer cell perturbation experiments.
    Full-text · Article · Aug 2013 · PLoS ONE
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    Full-text · Dataset · Jan 2013
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    ABSTRACT: Neuroblastoma is an embryonic tumor arising from immature sympathetic nervous system cells. Recurrent genomic alterations include MYCN and ALK amplification as well as recurrent patterns of gains and losses of whole or large partial chromosome segments. A recent whole genome sequencing effort yielded no frequently recurring mutations in genes other than those affecting ALK. However, the study further stresses the importance of DNA copy number alterations in this disease, in particular for genes implicated in neuritogenesis. Here we provide additional evidence for the importance of focal DNA copy number gains and losses, which are predominantly observed in MYCN amplified tumors. A focal 5 kb gain encompassing the MYCN regulated miR-17∼92 cluster as sole gene was detected in a neuroblastoma cell line and further analyses of the array CGH data set demonstrated enrichment for other MYCN target genes in focal gains and amplifications. Next we applied an integrated genomics analysis to prioritize MYCN down regulated genes mediated by MYCN driven miRNAs within regions of focal heterozygous or homozygous deletion. We identified RGS5, a negative regulator of G-protein signaling implicated in vascular normalization, invasion and metastasis, targeted by a focal homozygous deletion, as a new MYCN target gene, down regulated through MYCN activated miRNAs. In addition, we expand the miR-17∼92 regulatory network controlling TGFß signaling in neuroblastoma with the ring finger protein 11 encoding gene RNF11, which was previously shown to be targeted by the miR-17∼92 member miR-19b. Taken together, our data indicate that focal DNA copy number imbalances in neuroblastoma (1) target genes that are implicated in MYCN signaling, possibly selected to reinforce MYCN oncogene addiction and (2) serve as a resource for identifying new molecular targets for treatment.
    No preview · Article · Jan 2013 · PLoS ONE
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    ABSTRACT: Neuroblastoma (NB) is a paediatric tumour with a remarkable diverse clinical behaviour. Approximately half of the high stage aggressive tumours are characterized by MYCN gene amplification but our understanding of the role of MYCN in NB oncogenesis is incomplete. Previous studies have shown that MYCN expression is inversely correlated with expression of Dickkopf-3 (DKK3), a gene encoding an extracellular protein with presumed tumour suppressor activity, but direct MYCN regulation of DKK3 was excluded leaving the mechanism of regulation unexplained. Given the recently established role of MYCN-regulated miRNAs in downregulation of protein-coding genes and predicted seeds for miR-17-92 cluster members within the DKK3 3'UTR, we hypothesized that this mechanism would act in MYCN regulation of DKK3. To investigate this, we used a validated miR-17-92-inducible cellular system and could demonstrate robust downregulation of DKK3 mRNA and protein levels upon miR-17-92 overexpression. Next, two of the three predicted miRNAs, miR-19b and miR-92a, were shown to lower DKK3 protein levels, in addition to measurable DKK3 mRNA knock-down by miR-92a. Direct interaction between miR-19b or miR-92a and the 3'UTR of DKK3 was validated using luciferase reporter assays. In conclusion, this study demonstrates that the MYCN-induced downregulation of DKK3 results from direct upregulation of miR-17-92 components effecting both DKK3 mRNA stability and translation which further contributes to the pleiotropic oncogenic effect of elevated MYCN levels. The strict MYCN-mediated regulation of DKK3 is suggestive for an important downstream function of the MYCN protein and thus warrants further investigations to unravel the role of DKK3 in NB.
    Full-text · Article · Jun 2012 · International Journal of Cancer
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    ABSTRACT: Despite extensive analysis of the BRCA1 and BRCA2 genes, germline mutations are detected in <20% of families with a presumed genetic predisposition for breast and ovarian cancer. Recent literature reported RAD51C as a new breast cancer susceptibility gene. In this study, we report the analysis of 410 patients from 351 unrelated pedigrees. All were referred for genetic testing and we selected families with at least one reported case of ovarian cancer in which BRCA1&2 mutations were previously ruled out. We analyzed the coding exons, intron-exons boundaries, and UTRs of RAD51C. Our mutation analysis did not reveal any unequivocal deleterious mutation. In total 12 unique sequence variations were identified of which two were novel. Our study and others suggest a low prevalence of RAD51C mutations with an exception for some founder populations. This observation is in favor of the rare allele hypothesis in the debate over the nature of the genetic contribution to individual susceptibility to breast and ovarian cancer and further genome-wide studies in high risk families are warranted.
    No preview · Article · Feb 2012 · Breast Cancer Research and Treatment
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    ABSTRACT: One of the first and most important steps in the metastatic cascade is the loss of cell-cell and cell-matrix interactions. N-cadherin, a crucial mediator of homotypic and heterotypic cell-cell interactions, might play a central role in the metastasis of neuroblastoma (NB), a solid tumor of neuroectodermal origin. Using Reverse Transcription Quantitative PCR (RT-qPCR), Western blot, immunocytochemistry and Tissue MicroArrays (TMA) we demonstrate the expression of N-cadherin in neuroblastoma tumors and cell lines. All neuroblastic tumors (n = 356) and cell lines (n = 10) expressed various levels of the adhesion protein. The N-cadherin mRNA expression was significantly lower in tumor samples from patients suffering metastatic disease. Treatment of NB cell lines with the N-cadherin blocking peptide ADH-1 (Exherin, Adherex Technologies Inc.), strongly inhibited tumor cell proliferation in vitro by inducing apoptosis. Our results suggest that N-cadherin signaling may play a role in neuroblastoma disease, marking involvement of metastasis and determining neuroblastoma cell viability.
    Full-text · Article · Feb 2012 · PLoS ONE
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    ABSTRACT: Activating mutations of the anaplastic lymphoma kinase (ALK) were recently described in neuroblastoma. We carried out a meta-analysis of 709 neuroblastoma tumors to determine their frequency and mutation spectrum in relation to genomic and clinical parameters, and studied the prognostic significance of ALK copy number and expression. The frequency and type of ALK mutations, copy number gain, and expression were analyzed in a new series of 254 neuroblastoma tumors. Data from 455 published cases were used for further in-depth analysis. ALK mutations were present in 6.9% of 709 investigated tumors, and mutations were found in similar frequencies in favorable [International Neuroblastoma Staging System (INSS) 1, 2, and 4S; 5.7%] and unfavorable (INSS 3 and 4; 7.5%) neuroblastomas (P = 0.087). Two hotspot mutations, at positions R1275 and F1174, were observed (49% and 34.7% of the mutated cases, respectively). Interestingly, the F1174 mutations occurred in a high proportion of MYCN-amplified cases (P = 0.001), and this combined occurrence was associated with a particular poor outcome, suggesting a positive cooperative effect between both aberrations. Furthermore, the F1174L mutant was characterized by a higher degree of autophosphorylation and a more potent transforming capacity as compared with the R1275Q mutant. Chromosome 2p gains, including the ALK locus (91.8%), were associated with a significantly increased ALK expression, which was also correlated with poor survival. ALK mutations occur in equal frequencies across all genomic subtypes, but F1174L mutants are observed in a higher frequency of MYCN-amplified tumors and show increased transforming capacity as compared with the R1275Q mutants.
    Full-text · Article · Sep 2010 · Clinical Cancer Research
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    ABSTRACT: Neuroblastoma is a heterogeneous childhood tumor with poor survival outcome for the aggressive type despite intensive multimodal therapies. In this study, we aimed to identify new treatment options for neuroblastoma based on integrative genomic analysis. The Connectivity Map is a database comprising expression profiles in response to known therapeutic compounds. This renders it a useful tool in the search for potential therapeutic compounds based on comparison of gene expression profiles of diseased cells and a database of profiles in response to known therapeutic compounds. We have used this strategy in the search for new therapeutic molecules for neuroblastoma based on data of an integrative meta-analysis of gene copy number and expression profiles from 146 primary neuroblastoma tumors and normal fetal neuroblasts. In a first step, a 132-gene classifier was established that discriminates three major genomic neuroblastoma subgroups, reflecting inherent differences in gene expression between these subgroups. Subsequently, we screened the Connectivity Map database using gene lists generated by comparing expression profiles of fetal adrenal neuroblasts and the genomic subgroups of neuroblastomas. A putative therapeutic effect was predicted for several compounds of which six were empirically tested. A significant reduction in cell viability was shown for five of these molecules: 17-allylamino-geldanamycin, monorden, fluphenazine, trichostatin, and rapamycin. This proof-of-principle study indicates that an integrative genomic meta-analysis approach with inclusion of neuroblast data enables the identification of promising compounds for treatment of children with neuroblastoma. Further studies are warranted to explore in detail the therapeutic potential of these compounds.
    Preview · Article · Jun 2009 · Clinical Cancer Research
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    ABSTRACT: ArrayCGH is commonly used for high-resolution detection of copy-number alterations in tumours, allowing identification of chromosomal aberrations with prognostic or diagnostic relevance. Currently available arrayCGH platforms are still very expensive for analysis of large sets of samples. For this purpose, we have constructed a dedicated mini-array that is enriched for BAC/PAC clones in the prognostic important regions for neuroblastoma and that only covers a small area on the slide, allowing down-scaling of the labelling and hybridisation reagents and hence reducing the price. The mini-arrays were validated on neuroblastoma samples and comparison with high-resolution whole-genome arrayCGH data yielded complete concordant results.
    No preview · Article · Jul 2008 · Cancer letters

Publication Stats

256 Citations
125.81 Total Impact Points

Institutions

  • 2013-2015
    • Ghent University
      • Center for Medical Genetics
      Gand, Flemish, Belgium
  • 2008-2015
    • Universitair Ziekenhuis Ghent
      • Centre for Medical Genetics
      Gand, Flanders, Belgium